// 开关门
var btns=document.getElementsByTagName("button");
var uls=document.getElementsByTagName("ul");
for(var i=0;i<btns.length;i++){
    btns[i].onclick=function(){
        if(this.innerHTML=="+"){
            this.parentNode.nextElementSibling.style.display="block"
            this.innerHTML="-"
        }else{
            this.parentNode.nextElementSibling.style.display="none";
            this.innerHTML="+";
        }
    
    }
}


